The present invention relates to a process by which pitch that is suitable for use as a starting material for the manufacture of carbon fibers and other functional carbon materials is produced by polymerizing a condensed nuclear aromatic compound such as naphthalene, anthracene, phenanthrene or acenaphthene.
Mesophase pitch or isotropic pitch is produced by polymerization of naphthalene and other hydrocarbons. The process basically consists of heat-treating a hydrocarbon in the presence of a Lewis acid catalyst such as aluminum chloride at 100.degree.-300.degree. C., removing the added catalyst by such a technique as solvent extraction, precipitation or filtration, and further heat-treating the residue at 300.degree.-500.degree. C. Various versions of this method are described in Japanese Patent Publication No. 7533/1978, Journal of Materials Science, 20, pp. 3177-3183 (1985), and Japanese Patent Public Disclosure No. 83317/1986.
In all of these methods which involve the use of an aluminum chloride catalyst, the reaction is carried out at elevated temperatures, with the results so that a dehydrogenation reaction occurs as a side reaction to cause deterioration of the product pitch and that it is difficult to recover the used aluminum chloride catalyst from the pitch for further use. In addition, if the pitch produced is used as a precursor for the manufacture of carbon fibers, a trace amount of aluminum chloride or a derivative thereof remains in the carbon fibers being prepared, with the subsequent result that the strength and other properties of the fibers are considerably deteriorated during their calcination or graphitization. It is extremely difficult to remove all such aluminum chloride or derivatives thereof from the pitch or the fibers.